CHAPTER II 

 THE GRASSHOPPER'S COUSINS 



Nature's tendency is to produce groups rather than in- 

 dividuals. Any animal you can think of resembles in 

 some way another animal or a number of other animals. 

 An insect resembles on the one hand a shrimp or a crab, 

 and on the other a centipede or a spider. Resemblances 

 among animals are either superficial or fundamental. For 

 example, a whale or a porpoise resembles a fish and lives 

 the life of a fish, but has the skeleton and other organs of 

 land-inhabiting mammals. Therefore, notwithstanding 

 their form and aquatic habits, whales and porpoises are 

 classed as mammals and not as fishes. 



When resemblances between animals are of a funda- 

 mental nature, we believe that they represent actual blood 

 relationships carried down from some far-distant common 

 ancestor; but the determination of relationships between 

 animals is not always an easy matter, because it is often 

 difficult to know what are fundamental characters and 

 what are superficial ones. It is a part of the work of 

 zoologists, however, to investigate closely the structure of 

 all animals and to establish their true relationships. The 

 ideas of relationship which the zoologist deduces from his 

 studies of the structure of animals are expressed in his 

 classification of them. The primary divisions of the 

 Animal Kingdom, which is generally likened to a tree, are 

 called branches, or phyla (singular, phylum). 



The insects, the centipedes, the spiders, and the shrimps, 

 crayfish, lobsters, crabs, and other such creatures belong to 

 the phylum Arthropoda. The name of this phylum means 



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